Cassiopeia A
From Freepedia
| Observation data (Epoch J2000) | |
|---|---|
| Supernova type | Unknown |
| Remnant type | Shell |
| Host | Milky Way |
| Constellation | Cassiopeia |
| Right ascension | 23h 23m 26s |
| Declination | +58° 48′ |
| Galactic coordinates | G111.7-2.1 |
| Discovery | 1947 |
| Peak magnitude (V) | 6? |
| Physical characteristics | |
| Progenitor | Unknown |
| Progenitor type | Unknown |
| Colour (B-V) | Unknown |
| Notable features | Brightest radio source in the sky |
Cassiopeia A (Cas A) is a supernova remnant in the constellation Cassiopeia and the brightest extra solar radio source in the sky, with a flux of 2720 janskies at 1 GHz. It is believed to be approximately 300 years old but there are no historical records of any sightings of the progenitor supernova, probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth. Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and reabsorbed much of the light released as the inner star collapsed.
Cas A is 3C461 in the third Cambridge catalog of radio sources and G111.7-2.1 in the Green Catalog of Supernova Remnants.
It is known that the expansion shell has a temperature of around 50 million degrees, and is travelling at more than ten million miles per hour.
Cas A is the strongest radio source in the sky beyond our solar system, and was among the first discrete sources to be found, in 1947. The optical component was first identified in 1950. In 1979, it was predicted that Cas A had a black hole. (Shklovsky, 1979) In 1999, the Chandra X-Ray Observatory found a "hot point-like source" [1] close to the center of the nebula that is quite likely the neutron star or black hole predicted but not previously found. (Pavlov, et al, 2000)
Calculations working back from the currently observed expansion point to an explosion around 1667, although astronomer William Ashworth and others have suggested that the Astronomer Royal John Flamsteed may have inadvertently observed the supernova in 1680. At any rate, no supernova in the Milky Way has been visible to the naked eye from Earth since.
References
- Shklovsky IS (1979). Is Cassiopeia A a black hole?. Nature 279 (5715): 703. PMID 16067999
- Pavlov GG, Zavlin VE, Aschenbach B, Trumper J, Sanwal D (2000). The Compact Central Object in Cassiopeia A: A Neutron Star with Hot Polar Caps or a Black Hole?. Astrophysical Journal 531 (1): L53-L56. PMID 10673413
